A Yazidi member of parliament, Vian Dakheel, was also injured, along with New York Times reporter Alissa Rubin, who suffered 'an apparent concussion and broken wrists'.

War correspondent Ms Rubin, 56, was travelling on the Mi-17 helicopter with Australian photographer Adam Ferguson, who escaped unhurt.

Mr Ferguson's pictures show rescuers pulling men, women and children from the crumpled shell of the aircraft before carrying them to another helicopter which flew them off the mountain.

Mr Ferguson told the New York Times that the aircraft landed upside down, adding: 'If we had been another 50 metres higher we’d all be dead.'

Thousands of members of the Yazidi religious minority remain stranded in the mountains outside the town of Sinjar, which the Islamic State group captured earlier this month.

The Islamic extremists view the Yazidis as apostates and have vowed to kill all those who do not convert.

Their plight has prompted a multinational relief effort, with Iraqi and U.S. planes dropping dozens of crates of food and water.

Hundreds of Yazidi families are now finally reaching refugee camps across the border in Syria and Turkey after trekking for days in sweltering temperatures to escape the militants.

The U.S. military has meanwhile targeted the Islamic State group with a series of airstrikes aimed at protecting the Yazidis and slowing the advance of the militants toward Irbil, the capital of the largely autonomous Kurdish region.

Another 130 U.S. troops have arrived in Irbil on what the Pentagon described as a temporary mission to assess the scope of the humanitarian crisis on Sinjar Mountain.

David Cameron said that 'detailed plans are now being put in place' for an international mission to rescue stranded Yazidis in Iraq and that Britain 'will play a role in delivering it'.The Prime Minister spoke after returning from his family holiday to chair a meeting of the Government’s Cobra emergency committee to discuss the crisis.

But he insisted the UK involvement remained a humanitarian mission as he faced calls to directly arm Kurdish forces or join the US in air strikes against Islamic State (IS) extremist fighters. He also dismissed demands for Parliament to be recalled, saying it was unnecessary at this stage but would be kept under review.

Tornado jets are due to carry out reconnaissance missions of the area and the helicopters are en route to Cyprus ready for possible deployment in Iraq. But a number of military, religious and political figures are pressing Mr Cameron to go further and recall Parliament to allow MPs to vote on whether the UK should join the US in conducting air strikes on IS positions and arming the Kurds.

Australia's Prime Minister Tony Abbott meanwhile held open the possibility of sending a combat forces to Iraq in addition to military transport aircraft. But Australian defence minister David Johnston played down the prospect of an Australian combat force, saying the military had only committed to sending two C-130 Hercules transport planes for humanitarian aid drops to begin within two or three days.

France will send arms to Kurdish forces in the country, it has announced, in order to support their fight against Islamic State militants. It also added pressure on other European leaders to contribute to the effort earlier this week, when it called for an urgent meeting of EU foreign ministers to consider Kurdish requests for arms and an aid airlift to northern Iraq.

Meanwhile, Iraq's prime minister Nouri Maliki has said he will not relinquish power until a federal court rules on what he called a 'constitutional violation' by the president to replace him with a member of his own party.

The embattled premier has grown increasingly isolated, with Iraqi politicians and much of the international community lining up behind Haider Ibadi, a fellow member of his Shiite Dawa party tasked by the president with forming a new government that can unite the country in the face of an onslaught by Sunni militants.

'Holding on (to the premiership) is an ethical and patriotic duty to defend the rights of voters,' Mr Maliki said in his weekly televised address to the nation. 'The insistence on this until the end is to protect the state.

Mr Maliki vowed legal action against President Fouad Massoum for carrying out 'a coup' against the constitution.

'Why do we insist that this government continue and stay as is until a decision by the federal court is issued?' he asked, answering: 'It is a constitutional violation - a conspiracy planned from the inside or from out.'

Iraqi troops imposed heightened security in Baghdad today as international support mounted for a political transition.

Tanks and Humvees were positioned on Baghdad bridges and at major intersections, with security personnel more visible than usual. About 100 pro-Maliki demonstrators took to Firdous Square in the capital, pledging their allegiance to him.

Widespread discontent with Mr Maliki's divisive rule has reached the point where both Saudi Arabia and Iran - regional rivals often bitterly divided over Iraq - have expressed support for Mr Ibadi. The United States, the European Union and the United Nations have also expressed support for new leadership.

But Mr Maliki, whose bloc won the most votes in April elections, has thus far refused to step aside and rejected the appointment of Mr Ibadi, saying it was unconstitutional. Mr Ibadi was selected by the main Shiite alliance which includes Mr Maliki's bloc, but the Islamic Dawa party says Mr Ibadi 'only represents himself'.

Tanks and Humvees first rolled across the city early on Monday after Mr Maliki delivered a surprise midnight address first declaring his plans to take his complaint to federal court.

At a meeting between Mr Maliki and senior military commanders broadcast on state television yesterday, Mr Maliki said security forces should not get involved in politics, but raised the spectre of further unrest by saying that Sunni militants or Shiite militiamen might don military uniforms and try to take control of the streets.

He said: 'This is not allowed because those people, wearing army uniforms and in military vehicles, might take advantage of the situation and move around and make things worse.'

The turmoil stems from the rapid advance of the Islamic State group and allied Sunni militants across northern and western Iraq in June.

Fuelled by widespread Sunni discontent with Mr Maliki's rule, the insurgency seized Iraq's second largest city Mosul and routed the beleaguered armed forces. Thousands of people have been killed and more than 1.5 million displaced by the violence.

The militant advance slowed as they approached Baghdad and other majority Shiite areas, but the capital still sees near daily attacks.